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x402 rails / Arc

x402 on Arc: pay per model call in USDC on Circle's network

BlockRun is a launch partner for Arc, Circle's network: the same routing and pay-per-call API, settling each x402 payment in USDC on Arc at arc.blockrun.ai.

Get your agent on BlockRun Read the docs

How it works

Arc is Circle's own network, built around USDC as the native asset. BlockRun's Arc gateway serves the same catalog and the same OpenAI-compatible API as the Base and Solana gateways; what differs is where the 402 says to settle. An agent that holds USDC on Arc pays per call there, with no bridge and no second wallet.

The gateway lives at its own host with its own manifest and OpenAPI document, so an x402 client that discovers it reads Arc as the network in every advertised endpoint. Everything else — models, prices, free tier — is the BlockRun catalog.

Behind it is the BlockRun catalog: 78 chat models plus image, video, music and speech generation, search, market data and multi-chain RPC, priced per call. 6 open-weight models are free and need no wallet.

Setup

1. Base URL

https://arc.blockrun.ai/api/v1

2. Discover what is payable

curl https://arc.blockrun.ai/.well-known/x402

Questions

Is it the same API as blockrun.ai?
Yes. Same routes, same model ids, same request shapes; only the settlement network in the 402 differs.
Do I need Arc USDC to try it?
The free open-weight models need no payment at all. Paid calls settle in USDC on Arc.

Related

Two ways to run this

Get an API key

Sign in, get a key, and call the same endpoints with usage billed to your account. For teams that want one invoice instead of one wallet.

Get an API key 

Or let your agent pay per call, in USDC

No account, no API key. Three steps, and the last one is the request this page is about.

  1. 01
    Point your agent at BlockRun

    Install ClawRouter, or add the BlockRun MCP server to Claude Code, Cursor, Codex or OpenClaw. Any OpenAI-compatible client works too — change the base URL, nothing else.

    curl -fsSL https://blockrun.ai/ClawRouter-update | bash
  2. 02
    Fund a wallet with USDC

    Send USDC to a wallet on Base or Solana. There is no account to create and no API key to issue: the wallet is the account, and it pays per call.

  3. 03
    Use BlockRun from Arc

    The first call returns HTTP 402 with the exact price, your agent signs it, and the answer comes back. Payment settles on-chain; nothing is charged if the call fails.

    https://arc.blockrun.ai/api/v1
ClawRouter setup →How paying per call works →

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